Monday, October 17, 2011

Prey: Two killer whales circle the seal in the Antarctic before adopting a team technique to knock it off the ice

The seal feels perfectly safe lying on the Antarctic ice even if it is surrounded by a pod of killer whales.

But within minutes it has been knocked into the water in a clever team tactic before being killed.

These astonishing pictures show how the sea predators work together - and the technique provides meals for killer whales three out of every four times they use it, according to scientists.

Research has also found that the mammals - around 26ft in length and weighing more than six tonnes - carefully butcher the prey underwater, co-operating as they skin and dissect the seals.

Dr Robert Pitman, a marine scientist at the National Oceanic and Atmospheric Administration in California, took the stunning images of the pod going in for the kill.

He said: 'The killer whales were very good at knowing in advance if they were going to be able to wash a seal off a floe and they were always successful in getting the seal into the water.

'A couple of times the seal was washed off but managed to escape in the confusion, but not very often. From killer whale studies elsewhere we expected this kind of social interaction but it was the canniness of their hunting tactics that blew us away.'

Team tactic: Three killer whales create a huge wave as they head for the seal on the ice floe

Killer wave: The whales have created a wall of water to hit the ice and knock the seal off

Hanging on: The seal appears helpless to stop the wave washing it off the ice and into the water

Dr Pitman and his colleague Dr John Durban helped a BBC film crew capture their behaviour for the TV documentary series Frozen Planet, to be shown later this month.

They spent weeks tracking and recording the hunting behaviour in the pack ice off the coast of the Antarctica Peninsula.

In one attack, the whales charged in formation towards the ice from as far away as 150 feet, creating a wave in front of their bodies and a deep trough above their tails. A second larger wave formed above their pumping tails.

When they reached the ice, they dived under it, kicking their tails in a powerful stroke to create a large wave that washed over the ice and knocked the seal into the water where they could grab it and drown it.

Game over: The seal desperately tries to get back onto the ice, but the killer whales are ready to pounce

The whales prefer weddell seals, which can be up to 11 feet long,rather than the more aggressive crabeater and leopard seals.

Dr Pitman told the Sunday Telegraph that the whales deal with seals who try to hide among the ice after being knocked into the sea by creating shock waves with their tails to knock them out into the open water.

He said: 'The whales also blew streams of bubbles under the seals apparently trying to get them to bolt into open water where they wouldn't have a chance against the waiting killer whales.'